In an electric motor or the like using a ball bearing, reducing noise generated by the ball bearing is a particularly important subject. Hereinafter, the ball bearing is referred to simply as the bearing. As one of the conventional means for reducing such noises, Patent Literature 1 proposes a motor featuring a reduced noise that is achieved by suppressing its backlashes which is caused by a bearing in the direction of its rotary shaft, for example.
An outline of the means applied to conventional motors will be described with reference to FIG. 7. FIG. 7 is an enlarged cross-sectional view of a principal part of a conventional motor. As shown in FIG. 7, rotor 28 is equipped with core 24 and rotary shaft 23 fixed to core 24. Bearing 21 is attached to the end portion on the yoke 29 side of rotary shaft 23.
Bearing 21 includes inner ring 21a, outer ring 21b, and balls 21c. Outer ring 21b included in bearing 21 is pressed to fit into bearing holding part 29a included in yoke 29, and is held there. Inner ring 21a included in bearing 21 is fitted onto rotary shaft 23 with a gap therebetween. Between core 24 included in rotor 28 and inner ring 21a included in bearing 21, rotary shaft 23 is inserted into washer 22.
Washer 22 is disposed, with the washer being compressed in the axial direction of rotary shaft 23. In FIG. 7, the axial direction of rotary shaft 23 is the up-and-down direction of the figure. Inner ring 21a is applied with downward bias force Fa by washer 22, as shown in FIG. 7. Over the entire perimeter of a surface where washer 22 is in contact with inner ring 21a, inner ring 21a is uniformly applied with bias force Fa by washer 22. Bias force Fa applied by washer 22 pressurizes inner ring 21a included in bearing 21, in the axial direction. This pressurization eliminates gaps between inner ring 21a and balls 21c and gaps between balls 21c and outer ring 21b. As a result, the noise due to the backlashes of bearing 21 is suppressed, and the lifetime of bearing 21 is lengthened.